LeetCode 30 Day Challenge

#Day 15

Maximum Sum Circular Subarray

Given a circular array C of integers represented by A, find the maximum possible sum of a non-empty subarray of C.

Here, a circular array means the end of the array connects to the beginning of the array. (Formally, C[i] = A[i] when 0 <= i < A.length, and C[i+A.length] = C[i] when i >= 0.)

Also, a subarray may only include each element of the fixed buffer A at most once. (Formally, for a subarray C[i], C[i+1], ..., C[j], there does not exist i <= k1, k2 <= j with k1 % A.length = k2 % A.length.)

Example 1:

Input: [1,-2,3,-2]
Output: 3
Explanation: Subarray [3] has maximum sum 3

Example 2:

Input: [5,-3,5]
Output: 10
Explanation: Subarray [5,5] has maximum sum 5 + 5 = 10

Example 3:

Input: [3,-1,2,-1]
Output: 4
Explanation: Subarray [2,-1,3] has maximum sum 2 + (-1) + 3 = 4

Example 4:

Input: [3,-2,2,-3]
Output: 3
Explanation: Subarray [3] and [3,-2,2] both have maximum sum 3

Example 5:

Input: [-2,-3,-1]
Output: -1
Explanation: Subarray [-1] has maximum sum -1

Note:

1. -30000 <= A[i] <= 30000
2. 1 <= A.length <= 30000

C++ Solution:-

class Solution {
public:
int kadane(vector<int> arr, int n){
int dp[n];
dp[0] = arr[0];
for(int i=1;i<n;++i){
dp[i] = max(arr[i], dp[i-1]+arr[i]);
}
int max_sum = INT_MIN;
for(int i=0;i<n;++i){
max_sum = max(max_sum, dp[i]);
}
return max_sum;
}
int maxSubarraySumCircular(vector<int>& A) {
int n = A.size();
int max_kadane = kadane(A, n);

int overall_sum = 0;
for(int i=0;i<n;++i) overall_sum += A[i];

for(int i=0;i<n;++i) A[i] *= -1;
int max_wrap = overall_sum + kadane(A, n);
return (abs(max_wrap)>abs(max_kadane))?max_wrap:max_kadane;

}
};